Can second-order stimuli generate simultaneous motion contrast?

Abstract

Purpose. To test whether second-order motion stimuli can induce simultaneous motion contrast; in which a target grating is perceived to move in the opposite direction to two flanking test gratings. Magnitudes of motion contrast generated with first and second-order stimuli were compared. Methods. Two types of targets were used; static and counterphase gratings. First-order stimuli were luminance modulations of a uniform field, and second-order stimuli were contrast modulation of a random-dot filed. Both were sinusoidal grating of 0.25c/deg. The magnitude of motion induction was measured by a motion-nulling method using the double-random-staircase procedure. Results. When the target was a static grating, the second-order stimuli induced little or no motion contrast, while the first-order stimuli of the same effective contrast produced strong motion contrast. When the target was a counterphase grating both the first- and second-order stimuli produced strong motion contrast. Conclusions. Second-order stimuli can induce motion in a dynamic target but not in a static one. It is possible that, similar to the situation for motion aftereffects (Nishida & Sato, 1995, VR), the perception of motion contrast with static and dynamic targets are mediated by different mechanisms. The implications of the present results on the issue of second-order input to the relative motion processing system will be discussed. Show more